High efficiency reflector or searchlight



March 9, 1943.

- M. DECALIQN ama- EFFICIENCY REFLECTOR on SEARCHLIGHT Filed July 29. 1959 2 Sh eeis-Sheet 1 I 6% wm c o, QM (0015' Patented Mar. 9, 1943 HIGH EFFICIENCY REFLECTOR OR SEABCHLIGHT Maurice Dcalion- Paris, France; vested in the 4 Alien .Property Custodian Application July 29, 1939;:{Serial No. 287,396 In Luxemburg April 20, 1939 1 Claim.

The present invention relates to light reflectors, and, in particular, those intended to be used in connection with searchlights for automobile or other vehicles, which are limited, or the useful portion of which is limited by two curves, for instance two circumferences or portions of circumferences located respectively in parallel planes and the centersof which are on a common perpendicular to these planes, said perpendicular being generally called the axis of the reflector or Searchlight.

The parabolic projectors which are usually employed in connection with automobile searchlights do not permit, with the usual positioning of the source of light at the focus, of collecting as considerable a portion of the light flux emitted by said source of light as it maybe desired.

The object of the present invention is to provide a reflector with which the maximum-flux is utilized for a given depth of said reflector, and, consequently, to ensure a maximum 'efficiency of said reflector. the value of this maximum increasing when the depth of the reflector increases.

inversely, for a given value of the flux collected by the reflector, the invention permits of reducing the thickness or depth of the reflector.

According to the essential feature of the present invention, the light source is positioned, on

the axis of the reflector. at a point such that,

111 and d2 being the respective distances from this point to the edges of the reflector in a plane passing through the axis, R1 and R2 the distances of these edges to said axis, respectively, in the same plane, the following condition must be complied with: V

Of course, this condition may be complied with only in an approximate manner, since a function varies but little on either side of .itsmaximum.

It may also be complied with only for some points of the source of light when said source is not punctual, or for points which are different for various planes passing through the axis, it being understood that a source of light described as restricted is onein which the size of the source is reduced to the minimum compatible with practical considerations.

When this conditionis complied with, which corresponds to an increase of theflux collected by the reflector, the reflected light beam is generallynot cylindrical and there may ,bea. rather substantialconvergence or divergencefat the out- 7 put from the reflector.

In order to obtain a cylindrical beam or a beam of any other desired shape, with a determined distribution of the flux, I may combine with the reflector a lens or a system of lenses, either stepped or not, adapted to give the desired result.

Other features of the present invention will result from the following detailed description of some specific embodiments thereof.

Preferred embodiments of the present invention will be hereinafter described,.with reference to the accompanying drawings, given merely by way of example, and in which:

Fig. 1 is a diagrammatical view of a reflector in the form of a body of revolution, shown in section by a planepassing through its-axis;

Fig. 2 illustrates the geometrical construction of the-point where the source of light is to be located;

Fig. 3 gives, as a function of the depth of the reflector, the ratio (multiplied by 100) of the number of lumens collected by the reflector and the number of lumens emitted by the source; for a reflector made according to the: invention (curve in solid lines) and aparabolic reflector :(curve in dotted lines) ,in the case, taken by way of example, .in which therratio of R1'a11dJR2'iS equal to 100 divided by 24, that is to say 4.2;

Fig. 4 is a similardiagram corresponding to the case in which the same ratio is equal to divided by 24, that is to say 2.9;

Fig. 5 shows the construction of a reflector in the form of a body of revolution, of elliptical section, combined with divergent lens.

In the example of Fig. 1, ABJor A'B' represents the curvilinear are which, by rotation about axis )Qi, produces the surface of the reflector,

this surface being, in the present case, supposed to be a surface of revolution.

The useful surface of the-reflector is limited :by the two circumferences AA, BBC. the respective radii. of 'whichare. R2 and R1. The first circumference corresponds to the lamp carrier or tot-he end part of thelamp, or again tothe rounded part of the-bulb, that is the outline limited 'by the reflected rays tangent to saidlamp or to the tail part of the lamp; when the reflector is constituted by a silver-ed portion of the bulb, or again. to any other curve limiting theuseful surface of the reflector..

The second circumference BB isthe circumference of opening of the reflector, onwhich is generallymounted a door provided-With a glass which may be striated or not.

.These indications are given merelyby- Wayof non-limitative examples.

The main source of light being at point S the reflector will be made according to the invention if the following condition is complied with:

ever

This formula results from my researches on the question of determining what is the amount of flux collected by a reflector and it indicates that, if the source is of constant intensity in all directions, or at least of an intensity which can be considered as constant and maximum within the limits corresponding to lines SB and SA in a meridian plane, the absolute value of this intensity being possibly different for the respective meridian planes that are considered, the amount of flux received by the reflector is maximum for a given depth E of said reflector (this depth E being the distance between planes AA and BB along axis XX).

Considering the angles on and m2 made with axis XX by straight lines SB and SA, the formula may be written:

These formulas are true whatever be the form of the reflector, whether it is a body of revolution or not. 7

The location S of the light source (of one of its points in the radial plane that is being considered) which complies with this formula can be geometrically determined in a very simple that is to say:

manner. It suflices (Fig. 2) to determine, on straight line AB, two points C and D such that: 921 2- a CA DA R and to trace a circumference'having CD as a diameter. This circumference intersects the axis at the point S in question.

It is known that the flux collected by a parabolic reflector with the source located at the focus, passes through a maximum when radii R1 and R2 ar adapted to the parameter p of the paraboloid in such manner that:

cles in air, and for reasons of economy, R1 is reduced and as it is not possible to reduce R2 below a certain minimum, which is imposed for instance by the size of the rounded part of the bulb, parabolic reflectors have a low efficiency;

I have given by way of example, and in order fully to illustrate the invention, the curves representing the efiiciencies in lumens, that is to say the ratio multiplied by 100 of the number of lumens collected by the reflector and the total number of lumens emittedby the light source supposed to be of spherical shape and of constant intensity in all directions, as a function of the depth E of the reflector in both cases illustrated by Figs. 3 and 4.

The first case (Fig. 3) corresponds to a projector in which R1 is equal to 100 millimeters and R2 to 24 millimeters (these dimensions corresponding approximately to the so-called 220 mm. searchlight of the market).

The second case (Fig. 4) corresponds to a searchlight in which R1 is equal to 70 millimeters and R2 to 24 millimeters.

The solid line curve indicates the efficiency of searchlights in which the position of the source of light corresponds approximately to the formula above given.

The dotted line curve indicates the efliciency of the parabolic searchlights the respective parameters of which are indicated by an accessory scale.

It will be found that, in the first case (Fig. 3), for a depth of 95 millimeters, which is well within the admissible limits, a parabolic reflector has an efficiency of at most 61%.

The maximum efliciency of the parabolic reflector in the second case (Fig. 4) is only 48%.

With a reflector, either parabolic or not, in which R1 is equal to 100 and R2 to 24 (Fig. 3) and in which the source of light is positioned according to the invention, the efliciency will be 67.5% for the same depth of 95 millimeters.

On the other hand, in the same case in which R1 is equal to 100 and R2 to 24, a reflector made according to the present invention, that is to say corresponding to the solid line curve and of an efliciency equal to 61%, that is to say equal to the maximum emciency of the corresponding parabolic projector, will be of a depth of only millimeters instead of millimeters for the parabolic reflector.

The invention therefore permits:

a. For a reflector of given depth, of increasing the light flux that is collected;

1). For collecting a given flux, of obtaining a reflector of smaller depth.

Besides, these various advantages are all the more considerable as the ratio R1 F, is lower.

The efliciencies of the reflectors made according to the invention are always higher than, or.

at least equal to, those of parabolic reflectors. Besides, the efficiencies increase the more rapidly as a function of the depth as ratio i R2 is smaller.

The efiiciencies are equal only when the parameter p of the paraboloid complies with the following condition:

. 3 r 3 P 1 2( E-I' T) which does not correspond, especially if eiflciency is 48%.

With a reflector according to the invention of a depth equal to 70 millimeters the efliciency is 64%, that is to say higher than that of a parabolic reflector in which R is equal to 100 (Fig. 3).

With a depth of 100 millimeters, the efficiency would be 76%.

The difference between the ordinates of the respective solid lines curves and dotted lines curves of Figs. 3 and 4' indicates, for each depth of the reflector, the advantage that can be obtained, with respect to a parabolic reflector having the source of light at its focus, when the source of light is located in such manner that its position corresponds exactly to the formula above given.

But, obviously, I may be satisfied with only a portion of this advantage, for instance one half or one third thereof and, in this case, it will suffice to place the source at a distance of the point indicated by the above formula. One third of the possible theoretical advantage corresponds substantially to the curves traced in dash-anddot lines in Figs. 3 and 4. The zone ranging between this last mentioned curve and the solid line curve corresponds to positions of the light source for which still an important advantage would be obtained as compared with known reflectors.

The shape of the reflector may remain parabolic, but the position of the source, being then adapted to the values of R1 and R2, will be different from that of the focus and located, as a rule, on the other side thereof with respect to the apex of the reflector, whereby the beam will no longer be stigmatic to infinity. This convergent beam can be corrected by means of a lens or a system of lenses, mounted on the output opening of the reflector.

However, for this correction, it is more advantageous to have a stigmatic beam and, consequently, it is preferable to take as meridian AB of the reflector another curve of the second degree, an ellipse or an hyperbola having one of its foci at point S determined by the above formula or approximately determined as above explained.

The curvature of the reflector may also be determined in such manner as to form several images S of point S, on the axis of the reflector, these images being adapted to form a line or a system of lines, or a system of points.

In this case, the reflector may also be. either wholly or partly, of stepped outline.

When are AB is an arc of an ellipse (case shown by Fig. 5), the second focus of the ellipse is located at S, ahead of S. The beam sup plied by the reflector will then be convergent toward S, and, in order to make it cylindrical, there can be associated therewith a divergent lens L having its object focus at S.

Advantageously, I will take a meridian of the reflector, an arc of ellipse AB the longer axis of which is substantially the axis of the reflector and the shorter axis of which is diameter BB. The depth of the reflector is then determined.

If arc AB were an arc of an hyperbola, the second focus would be located on the left hand side of S. The beam supplied by the reflector would then be divergent and would issue from said reflector as if it came from said second focus. It might be made cylindrical by means of a convergent lens the object focus of which would coincide with said focus of the hyperbola.

In the drawings, I have considered the case of a reflector constituted by a body of revolution limited by two circumferences, but the reflector can, according to the invention, be constituted by a body which is not of revolution. It sufiices to have the condition above set forth complied with either exactly or approximately in each of the radial planes passing through the axis.

This may lead to limiting the reflectors by two curves AA different from circles and/or making use of points S which do not coincide for the respective planes.

The points S corresponding to the various planes will be distributed, for instance, over a small length of axis XX, and it will sufi'ice to have a nonpunctual source which occupies this length or a portion of this length.

Furthermore, the invention may be applied only to a portion of the reflector, for instance limited by two planes passing through axis XX, or in any other way.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and eflicient embodiments of the present invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as comprehended within the scope of the appended claim.

What I claim is:

A device of the type described, which comprises, in combination, a restricted source of light, and a concave reflecting surface having an axis passing through said source and the concavity of which is toward said axis, said suri face being limited by two parallel planes per pendicular to said axis and being so shaped as to reflect the light rays from said source in the form of a convergent beam the caustic curve of which is ahead of the front edge of said surface, said source of light being located at a point of said axis such that the cube of the ratio of the distances from said point to the edges of said surface, in an axial plane, is equal to the square of the ratio of the distances from said edges to said axis in the same plane.

MAURICE DECALION. 

